1. Field of the Invention
This invention relates to a control valve device having control valves connected in parallel between one fixed displacement pump and many oil actuators to control and drive the actuators.
2. Description of the Prior Art
Pressure compensated flow control valves connected in parallel with one fixed displacement pump have been used, e.g., such valves as shown in the diagrams in FIG. 8 and FIG. 9, but they have not yet been found to be satisfactory for use because of the following points.
In a device such as shown in FIG. 8, when all directional valves are in neutral position, pilot oil pressure at the spring side of the relief valve is exhausted to the oil tank and the pump discharge oil pushes the relief valve spool against the spring to open the relief valve and to discharge all the flow to the oil tank. When any one of the directional valves is in an operating position, the working pressure thereof acts on the spring side of the relief valve to move it in the closing direction so as to increase the pump discharge pressure. But when more than one of the directional valves are in operating positions, pilot pressure acting on the relief valve tends to be the average working pressure of the operating directional valves, and it becomes difficult to hold the pump discharge at the highest required pressure, and flows to valves requiring lower pressure tend to increase above the desired flow rate because of higher pump discharge pressure. Therefore regular simultaneous operation is impossible.
In a device such as shown in FIG. 9, as the pilot pressure on the spring side of the spool of the relief valve there is selected, through a shuttle valve, the highest pressure among the working pressures of the operating control valves. Of this highest pressure, only the operating control valve with the highest working pressure can operate regularly, and other operating valves are fed with higher pressure than each requires. Therefore additional manual control operation is necessary to lower the higher pressure supplied to the respective required pressures, and the desired flow rate cannot be held automatically if the working pressure varies. Consequently regular simultaneous operation is also impossible in this case.
In another arrangement of such a control device, a counter balance valve as shown in the diagrams of FIG. 10 and FIG. 11 can be added to accomodate a pressure rise and pressure variation which occurs in the return passage from the oil actuator. An external pilot type valve is shown in FIG. 10, and it operates in response to a pressure variation in feed passage to the control valve from the actuator to produce an opposite variation in the passage with the valve in it, and the operation is delayed and becomes a source of troublesome hunting action. A satisfactory valve of this type is nothing new. An internal pilot type valve is shown in FIG. 11 and it operates in response to pressure variation in the return passage from the actuator to the control valve in which the control valve itself is located so as to open the counter balance valve when the pressure increases. Hunting action does not occur with this arrangement, but the pressure rise in the return passage is added to the pump pressure loading to increase power consumption, and this type of counter balance valve is not usually used.